BP uses a different frozen pipeline to make the opposite point, that it couldn't have foreseen what would happen in 2009. Its example is from 2007 and involved a pipeline that, like the one in 2009, was feeding into its Lisburne Production Center. When efforts to thaw the pipeline in 2007 failed, BP let it sit until spring, when BP says it thawed naturally with no spilled crude or other environmental damage.

The situation didn't end so well in 2009. Excess pressure from expanding ice blew a 2-foot hole in that Lisburne pipeline. BP has said 13,500 gallons of crude spilled onto the snowy tundra, though testimony in the hearing indicates the amount could have topped 15,000 gallons.

The circumstances of all three frozen pipelines have been detailed in a probation hearing in U.S. District Court in Anchorage that began Nov. 29. BP has been on criminal probation since 2007 for a much bigger spill in 2006.

Prosecutors say the 2009 spill amounts to a new environmental crime and that BP's behavior was negligent. They want BP's probation revoked and the judge to order new fines and another term of probation.

But BP says the Lisburne pipeline had operated properly for almost 25 years and that the company couldn't have known what was coming.

BP has not been charged criminally for the 2009 spill but that's not required for U.S. District Judge Ralph Beistline to rule on whether the company violated its probation.

John Eldred, BP vice president of safety and operational risk, testified for the company Tuesday.

At issue is an 18-inch line that carried a mix of oil, natural gas and water to be separated at the processing plant.

Eldred said it was reasonable for BP operators and engineers to consider the 2007 incident as they evaluated whether the 18-inch Lisburne line was at risk of freezing and rupturing.

BP had never had a large-diameter line like that rupture, Eldred said under questioning by BP lawyer Jeff Feldman.

The Lisburne pipe that froze in 2007 was a 14-inch line similar to the 18-inch line. BP had tried to shut it in for maintenance but a valve failed to close completely and fluids seeped in and froze up, Eldred said. BP tried to thaw it by pumping in methanol, and then using a heat conductor. When nothing worked, BP decided to leave it until spring, he said.

If anything, the bigger line was at less risk of freezing and rupturing because it carried more fluids that would better retain heat, Eldred testified.

Then there was the 2001 incident, what's known as the D-pad Prudhoe Bay spill. In that case, a mechanical valve at the perimeter of a much smaller, 6-inch pipeline closed on its own, stopping the flow of oil, Eldred said. An alarm signaled the problem to the control center but the crew there didn't react, he said. The drilling operator wasn't alerted.

Once BP realized the pipe was frozen, crews pumped in methanol and crude oil to thaw it, not knowing that it had already split like a garden hose, BP spokesman Steve Rinehart said during a break in the hearing. About 9,000 gallons of crude spilled, he said.

That situation -- which the government contends BP should have learned from -- was different than the 2009 incident, Eldred testified. The 18-inch Lisburne pipeline is about 10 times bigger than the D-pad line. It carries much more natural gas along with oil. It's part of a pipe system fed by dozens of wells, which tend to mix into a hotter blend than that produced from the three or four wells that feed the D-pad line, he said.

But under cross-examination by assistant U.S. Attorney Aunnie Steward, Eldred acknowledged similarities: Both pipes froze after oil stopped flowing. Both were looped with a companion line that masked problems. Both had temperature sensors positioned inside the heated modules. The D-pad line's temperature sensors were moved outside but the same change was not made at Lisburne, witnesses have testified.

Besides the circumstances of the frozen Lisburne pipeline, the case also concerns whether the spill occurred "in U.S. waters," a necessary element to find a criminal violation of the federal Clean Water Act.

That part of the case is extremely technical. Beistline has asked witnesses, and lawyers, to slow down.

The hearing resumes today and may wrap up. If Beistline finds that BP violated its probation, a separate hearing would likely be held to decide any punishment.